The present invention relates to the manufacture of semiconductor devices and more particularly to apparatus for coating semiconductor wafers.
As is understood by those skilled in the art, the manufacture of semiconductor devices, such as integrated circuits, is typically accomplished by microlithographic or photorepeater techniques which involve exposing a circuit pattern on the surface of a semiconductor wafer which has been coated with a photosensitive resist. After exposure, the resist is developed to reveal the desired pattern for subsequent processing steps. Both the coating and the developing must be precisely controlled in order to repeatably obtain the desired results. As is also understood, both the resist coating and the developing process typically involve the spreading of a thin film of liquid over the surface of the wafer in as uniform a manner as possible.
Particularly in the resist coating operations, it is highly desirable to minimize the amount of coating material used since the materials employed are typically quite expensive. In previously known coating processes, a quantity of resist material is placed on the surface of a wafer and the wafer is then spun, initially at a relatively low speed to spread the material and then at a relatively high speed to reduce the layer to the desired thin film. It has typically been quite difficult to cause the initial spread of the resist to proceed evenly from the center of the wafer to the periphery so that an excess of material was necessary to insure that all portions of the wafer were covered.
Among the several objects of the present invention may be noted the provision of novel apparatus for coating semiconductor wafers with a thin film; the provision of such apparatus which requires a minimum of coating material to effect coating; the provision of such apparatus which provides improved uniformity of coating; the provision of such apparatus which is highly reliable and which is of relatively simple and inexpensive construction. Other objects and features will be in part apparent and in part pointed out hereinafter.